System for indicating the position of a surgical probe within a head on an image of the head

ABSTRACT

A system for determining a position of a probe relative to an object such as a head of a body of a patient. The head includes a surface such as a forehead having a contour. Cross sectional images of the head are scanned and stored as a function of the forehead contour. If the forehead contour does not appear in the scan images, then the position of the forehead contour relative to the scan images is determined with an optical scanner and a ring. During surgery, the optical scanner also determines the position of the forehead relative to the ring. An array for receiving radiation emitted from the probe and from the ring generates signals indicating the position of the tip of the probe relative to the ring. A stereotactic imaging system generates and displays an image of the head corresponding to the measured position of the tip of the probe. The system may also display scan images from different scanning technologies which scan images correspond to the same position in the head.

This application is a continuation of U.S. patent application Ser. No.08/477,561 filed Jun. 7, 1995, now U.S. Pat. No. 5,891,034. ApplicationSer. No. 08/477,561 is a continuation of U.S. patent application Ser.No. 08/053,076 filed Apr. 26, 1993, now abandoned. Application Ser. No.08/053,076 is a continuation-in-part of U.S. patent application Ser. No.07/858,980, filed May 15, 1992, now abandoned, which is a national stageapplication based on PCT/US91/07745, filed Oct. 17, 1991, which PCT is acontinuation-in-part of U.S. patent application Ser. No. 07/600,753,filed Oct. 19, 1990, now abandoned. Application Ser. No. 08/053,076 isalso a continuation-in-part of U.S. patent application Ser. No.07/909,097, filed Jul. 2, 1992, now U.S. Pat. No. 5,383,454, which is acontinuation of U.S. patent application Ser. No. 07/600,753, filed Oct.19, 1990, now abandoned.

BACKGROUND OF THE INVENTION

Precise localization of position has always been critical toneurosurgery. Knowledge of the anatomy of the brain and specificfunctions relegated to local areas of the brain are critical in planningany neurosurgical procedure. Recent diagnostic advances such ascomputerized tomographic (CT) scans, magnetic resonance imaging (MRI)scanning, positron emission tomographic (PET) scanning, andmagnetoencephotographic (MEG) scanning have greatly facilitatedpreoperative diagnosis and surgical planning. However, the precision andaccuracy of the scanning technologies have not become fully available tothe neurosurgeon in the operating room. Relating specific structures andlocations within the brain during surgery to preoperative scanningtechnologies has previously been cumbersome, if not impossible.

Stereotactic surgery, first developed 100 years ago, consists of the useof a guiding device which channels the surgery through specific parts ofthe brain as localized by preoperative radiographic techniques.Stereotactic surgery was not widely used prior to the advent of modernscanning technologies as the injection of air into the brain wasrequired to localize the ventricles, fluid containing chambers withinthe brain. Ventriculography carried a significant complication rate andaccuracy in localization was marginal.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a system which candetermine the position of a probe within an object and display an imagecorresponding to the determined position. It is a further object of thisinvention to provide a system which can determine the position of anultrasound probe relative to an object and, still further, which candisplay scan images from other scanning technologies corresponding tothe scan images produced by the ultrasound probe. It is a further objectof this invention to provide a system which can relate scan images of anobject produced with one technology to scan images of the same objectproduced with another technology.

The invention comprises a system for indicating a position within anobject. The system includes reference points means in fixed relation tothe object. Means generates images of the object, said images includingreference images corresponding to the reference points means. The systemalso includes reference means located outside the object and a probeincluding a tip. First means determines the position of the tip of theprobe relative to the reference means. Second means measures theposition of the reference points means of the object relative to thereference means, so that the position of the tip relative to thereference points means of the object is known. Means translates thedetermined position of the tip of the probe into a coordinate systemcorresponding to the images of the object. Means displays an image ofthe object which corresponds to the translated position of the tip ofthe probe.

The invention also comprises a system for indicating a position within abody of a patient. The system includes reference points means in fixedrelation to the body. Means generates images of the body, said imagesincluding reference images corresponding to the reference points means.The system further includes reference means located outside the body anda probe including a tip. First means determines the position of the tipof the probe relative to the reference means. Second means determinesthe position of the reference points means of the body relative to thereference means, so that the position of the tip relative to thereference points means of the body is known. Means translates thedetermined position of the tip of the probe into a coordinate systemcorresponding to the images of the body. Means displays an image of thebody which corresponds to the translated position of the tip of theprobe.

The invention also comprises a method for indicating a position of a tipof a probe which is positioned within an object such as a body on imagesof the body wherein the body and the images of the body includereference images corresponding to a reference point. The method includesthe steps of determining the position of the tip of the probe relativeto a reference means having a location outside the body; determining theposition of the reference points of the body relative to the referencemeans so that the position of the tip relative to the reference pointsof the body is known; translating the determined position of the tip ofthe probe into a coordinate system corresponding to the images of thebody; and displaying an image of the body which corresponds to thetranslated position of the tip of the probe.

The invention also comprises a system for determining a position of anultrasound probe relative to a part of a body of a patient wherein theprobe is positioned adjacent to and scanning the body part. An array ispositioned in communication with the probe. First means determines theposition of the ultrasound probe relative to the array. Second meansdetermines the position of the body part relative to the array. Meanstranslates the position of the ultrasound probe into a coordinate systemcorresponding to the position of the body part.

The invention also comprises a system for relating scan images of a bodyof a patient. The scan images are produced from first and secondscanning technologies. The system includes reference points means infixed relation to the body. Means relates the first scanned images tothe reference points means. Means relates the second scanned images tothe reference points means. Means selects a particular first scannedimage. Means determines the position of the particular first scannedimage relative to the reference points means. Means generates a secondscanned image which has the same position relative to the referencepoints means as the determined position so that the generated secondscanned image corresponds to the particular first scanned image.

The invention also comprises apparatus for indicating a positionrelative to a body of a patient. The apparatus comprises radiopaquemarkers and means for noninvasively supporting the markers on thesurface of the skin of the body. The supporting means may comprise asheet of material overlying the body, and means on the sheet of materialfor supporting the markers.

The invention may be used with a scanner for scanning a body part of apatient in order to generate images representative of the body part. Theimprovement comprises means for marking the surface of the skin on thebody part with a radiopaque material, whereby the generated imagesinclude images of the marking means.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective illustration of a reference ring of the priorart which is mounted by uprights to a patient's head to support thecylindrical frame structure of FIG. 1B or the ring 306 of FIG. 3B.

FIG. 1B is a perspective illustration of a cylindrical frame structureof the prior art which is mounted around a patient's head during thescanning process.

FIG. 1C is a plan view according to the prior art of the rods of thecylindrical frame structure of FIG. 1B taken along a plane midwaybetween the upper and lower rings.

FIG. 1D is a perspective illustration of the coordinate system of athree dimensional scanned image.

FIG. 2A is a perspective view of the caliper frame of the prior art usedto target a position in the brain and to determine a position in thehead relative to the phantom base.

FIG. 2B is a perspective view of the caliper frame of the prior art ofFIG. 2A illustrating its angles of

FIG. 2C is a block diagram of the steps involved in the prior artprocess of determining the position of a probe relative to the scannedimages so that the image corresponding to the probe position can beidentified and viewed by the surgeon.

FIG. 2D is a perspective illustration of a three dimensional coordinatesystem of a probe.

FIG. 3A is a block diagram of one system of the invention for indicatingthe position of a surgical probe within a head on an image of the head.

FIG. 3B is a perspective schematic diagram of a microphone array, probeand base ring according to one system of the invention.

FIG. 3C is a block diagram of the steps involved in the processaccording to the invention for determining the position of a surgicalprobe relative to the scanned images so that the image corresponding tothe probe position can be identified and viewed by the surgeon.

FIG. 3D is an illustration showing three reference points on a head foruse as a frame of reference during preoperative scanning and surgery.

FIG. 4A is a perspective schematic diagram of an infrared detectorarray, probe, reference bar, clamp and optical scanner according to onesystem of the invention.

FIG. 4B is a block diagram of a system for use with the apparatus ofFIG. 4A for determining the contour of a forehead.

FIG. 5 is a flow chart of the translational software for translatingcoordinates from the probe coordinate system to the scanned imagecoordinate system according to the invention.

FIG. 6A is a perspective schematic diagram of a detector array,reference bar, clamp and ultrasound probe according to one system of theinvention;

FIGS. 6B and 6C illustrate ultrasound and scanned images, respectively.

FIG. 7 illustrates the orientation of the base ring with a scanningplane for relating the position of a probe with a scanned image or forinterrelating the scanned images of different scanning technologieswhich correspond to a common position in the head according to onesystem of the invention.

FIG. 8 illustrates the use of a remote depth finder for determining thecontour of a forehead.

FIGS. 9 through 11 illustrate apparatus including a cap and grommets forholding radiopaque markers during scanning.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With the advent of modern scanning equipment and techniques, severalstereotactic systems have been developed and are presently available.These stereotactic systems allow a surgeon to localize specific pointsdetected on CT, MRI, PET, or MEG scans which have been previouslygenerated prior to the surgical procedure being performed. InParticular, the stereotactic systems allow the selection of specificpoints detected on the scans to be localized within the brain by thesurgeon during the surgical procedure using a mechanical device.

In use, the prior art stereotactic systems often require a base such asa ring 120 (also known as a BRW head ring) in FIG. 1A. Ring 120 isfirmly attached to the patient's skull via uprights 122 and sharp pins124 throughout scanning and surgery.

During scanning, some form of localizing device, such as a cylindricalstructure 100 in FIG. 1B, is attached to ring 120. Structure 100comprises an upper circular ring 102 in parallel with a lower circularring 104. Lower ring 104 is mounted to reference ring 120 so that thethree rings 102, 104 and 120 are in parallel planes. Rings 102 and 104are interconnected by six vertical rods 106 and three diagonal rods 108.These specific marking rods are also called fudicels. The three diagonalrods 108 diagonally interconnect rings 102 and 104. Any plane orthogonalto an axis 110 of structure 100 which passes through structure 100 willcreate a unique pattern of six cross sectional views of rods 106 andthree cross sectional views of rods 108. The resultant spacing betweenthe diagonal and upright rods defines a unique orthogonal plane withinstructure 100. FIG. 1C shows, for example, the spacing of the rods whenthe position of the scan plane 112 is parallel to and midway betweenrings 102 and 104 of structure 100.

After the scanning process, the images obtained are analyzed and theposition of rods 106 and 108 shown in the images is measured. By knowingthe position of rods 106 and 108, the specific location of a scan withrespect to structure 100 and therefore with respect to base ring 120 candetermined. As shown in FIG. 1D, the scans can be arranged within ascanned image coordinate system 125 with reference plane RP set in fixedrelation to the position of ring 120. A scan plane SP can be definedwithin the scanned image coordinate system 125 by at least threereference points SP1, SP2 and SP3 located on the head of the patient. Byassociating a scan image with a scan plane SP in the scanned imagecoordinate system, a point on the scan can be identified with a point inthe patient's head.

During surgery, the surgeon can use the stereotactic system to calculatea specific position within the brain corresponding to a scan image andthen target that portion of the brain with a probe. First, the structure100 used during scanning is removed from ring 120 and a speciallydesigned caliper frame 200, as illustrated in FIG. 2A, is attached toring 120. Frame 200 holds a surgical probe 202 which is positioned on anarch 206 for insertion into the patient's head. Frame 200 indicates thealpha, beta, gamma and delta angles on scales 208, 210, 212 and 214 fordirecting probe 202 to a particular target, as shown in FIG. 2B. Thedistance 216 from the tip of probe 202 to arch 206 is also determined. Acomputer is then used to correlate the position of the targeted scanimage in the scanned image coordinate system with the correspondingangles alpha, beta, gamma and delta and distance 216 on frame 200 toenable the surgeon to apply the probe to the targeted area of the brain.A target picked out on a scan of a specific image can be approached witha fair degree of accuracy using this surgical procedure.

In the past, the surgeon has also used the stereotactic system inreverse in order to determine the position of the probe 202 in the brainrelative to the scanned images so that the scan image corresponding tothe probe position can be identified and viewed. To do this, the surgeonagain attaches frame 200 to ring 120. Probe 202 is then positioned inframe 200 and inserted into the brain. Frame 200 is then removed fromring 120 and mounted to a phantom base 250 in a manner as illustrated inFIG. 2A. Phantom base 250 has a coordinate system (X₁, Y₁, Z₁).Generally, caliper frame 200 identifies a point 201 over phantom base250. A pointing device 252 is positioned to have its tip 254 at point201. The X₁ -Y₁ plane of phantom base 250 is parallel to the plane inwhich the reference points RP1, RP2 and RP3 are located. The (X₁, Y₁,Z₁) coordinates define the position of point 201. As a result, theposition of point 254 with respect to the X₁ -Y₁ plane and, therefore,with respect to the reference plane RP is now known. A computer is usedto calculate the specific position within the brain and the particularscan which corresponds to the calculated position can now be accessedand viewed on a scanning system. This prior art process is shown indiagram form in FIG. 2C.

After this cumbersome and time-consuming process, the surgeon has nowdetermined the position of the tip 201 of probe 202 with respect to thescanned images and can now view the image corresponding to the probeposition to decide the next step in the surgical procedure. This entireprocess takes approximately ten to fifteen minutes and increases therisks of intraoperative contamination as the base of frame 200 isnonsterile. Because of these considerations, this surgical procedure isnot commonly performed.

Although stereotactic surgery as performed with the apparatus of theprior art allows a surgeon to be guided to a specific point withaccuracy, it has not been particularly useful in allowing the surgeon toidentify the particular location of a probe within the brain at anypoint during the surgical process. Frequently in neurosurgery, braintumors or other target points within the brain are indistinguishablefrom surrounding normal tissue and may not be detected even with the useof frozen sections. Moreover, with modern microsurgical techniques, itis essential that the neurosurgeon identify specific structures withinthe brain which are of critical functional importance to the patient.The boundaries of these structures must be accurately defined andspecifically known to the surgeon during the surgical process. In thisway, these tissues will not be disturbed or otherwise damaged during thesurgical process which would otherwise result in injury to the patient.The minimal accuracy afforded by stereotactic surgery is generallyinsufficient for modern microsurgical techniques. Consequently,stereotactic surgery is not generally available to the majority ofpatients undergoing surgery.

The present invention solves these problems by allowing the surgeon toretrieve and display quickly the scanned image which corresponds to thecurrent position of a tip 301 of a surgical probe 302. A cursor appearson the displayed scan to show the position of probe tip 301 within thedisplayed scan. FIGS. 3A-3C and 5 illustrate a system of the inventionwhich includes sound emitters 360 and 370 and microphone detectors 350and associated hardware to determine the position of probe tip 301relative to a reference ring 306 on the patient's head. Because theposition of the scanned images relative to reference ring 306 is knownfrom the scanning procedure, the position of probe tip 301 relative tothe scanned images is known and the relevant image can be displayed.FIGS. 3A and 4A-8 illustrate a system of the invention which includesinfrared emitters 540 and 545 and detectors 550 in place of the soundemitters 360, 370 and microphone detector 350 for determining theposition of a reference bar 548 and a probe tip 541. A computer 396 andan infrared scanner 380 relate the scanned images to the shape of theforehead and relate the shape of the forehead to the position ofreference bar 548. Reference bar 548 is then associated with the scannedimages through the forehead shape without the use of the cylindricalreference frame 100 during scanning. The use of the forehead shape as areference point also allows the scanned images from different scanningtechnologies to be interrelated. As an alternative to reference ring 306and reference bar 548 described above, FIG. 3D uses reference pins 307affixed to the skull for determining the position of the patient's headduring surgery. As a further alternative, FIGS. 9-11 use a removable capfor holding markers during scanning. The positions of the markers aremarked on the head for later use during surgery in registering thesurgical space with the scan images. FIG. 6 includes an ultrasound probe500 for use during surgery. Other advantages are also provided as morefully described below.

In relating the position of a probe tip e.g., probe tip 301, to ascanned image, it can be seen in FIGS. 1D and 2D that the surgeon mustknow the specific location of tip 301 with respect to the scanned imagecoordinate system (X₀, Y₀, Z₀) of the scans that were preoperativelyperformed. In other words, probe tip 301 has a particular coordinatesystem (X₂, Y₂, Z₂) which is illustrated in FIG. 2D. Ideally, thesurgical probe coordinate system (X₂, Y₂, Z₂) must be related to thescanned image coordinate system (X₀, Y₀, Z₀). The prior art asillustrated in FIG. 2B has suggested relating these coordinate systemsvia the phantom base coordinate system (X₁, Y₁, Z₁). However, as notedabove, this relational process is inaccurate, time-consuming andcumbersome. The invention uses a 3D digitizer system to locate theposition of probe tip 301 within the probe coordinate system (X₂, Y₂,Z₂) and to relate it to the scanned image coordinate system (X₀, Y₀,Z₀).

FIGS. 3A and 3B show a microphone array 300, a temperature compensationemitter 304, a surgical probe 302, and a base ring 306. Microphone array300 includes a plurality of microphones 350 which are preferably spacedone meter apart. Microphones 350 may be attached to the operating lightabove the patient's head in direct line of sight of all of the emitters360 and 370. Microphones 350 thereby detect the sound emitted from theemitters. Surgical probe 302 preferably is a surgical coagulatingforceps such as a bipolar coagulating forceps. Probe 302 could also be adrill, suction tube, bayonet cauterizing device, or any other surgicalinstrument modified to carry at least two sound emitters 360 thereon fordetermining position. Emitters 360 on probe 302 are essentially coaxialon an axis 362 with tip 301. Emitters 360 are in line and immediatelybelow the surgeon's line of sight so that the line of sight is notblocked. Probe 302 has a bundle of wire 364 attached thereto orconnection to an electrical power source. The wires required to energizeemitters 360 are combined with bundle 364. The surgeon is familiar withhandling such a probe connected to a wire bundle; therefore, thisapparatus does not inconvenience the surgeon. During surgery, ring 306is affixed to the reference ring 120 attached to the patient's head andis essentially coplanar with it. Ring 306 includes a plurality ofemitters 370 which are preferably positioned 90 degrees apart with thecenter emitter being located at the anterior of the head. This permitsring 306 to be mounted around the head so that all three emitters are inline of sight with array 300.

In use, the position of each of emitters 360 and 370 is determinedindividually in order to determine the position of the devices to whichthe emitters are attached. This is accomplished by rapidly energizingthe emitters one at a time in a predetermined sequence and measuring thetime required for the individual sounds to reach each of microphones 350in array 300. A 3D digitizer 312 controls this operation through asignal generator 308 and a multiplexer 310. Digitizer 312 may be anoff-the-shelf Model GP-8-3D three dimensional sonic digitizer producedby Scientific Accessories Corporation. Under the control of digitizer312, multiplexer 310 applies an energizing signal from signal generator308 first to a temperature compensation emitter 304, then sequentiallyto emitters 370 on ring 306, then sequentially to emitters 360 on probe302. During this time, digitizer 312 receives and digitizes the outputsignals produced by microphones 350 in response to the energizations ofthe emitters. The digitized output signals are output to a computer 314.

Computer 314, following the flow chart shown in FIG. 5 as more fullydescribed below, is programmed with the predetermined pattern and timingfor energizing emitters 360 and 370. Computer 314 includes a spatialacquisition and recording (SAR) program 316 which acquires and recordsspatial coordinates based on the digitized signals. For example, the SARprogram 316 may be the SACDAC program licensed by PIXSYS of Boulder,Colo. SAR program 316 measures the time of transmission from each of theemitters to each of the microphones 350. By comparing these times, SARprogram 316 calculates the position of each of emitters 360 and 370.Since ring 306 contains three emitters 370, SAR program 316 cancalculate the position of ring 306 through standard geometriccomputations. This plane essentially defines the reference plane of thescan images because it is coplanar with the reference points RP1, RP2and RP3 in the scanning coordinate system of FIG. 1D. Similarly, sinceprobe 302 contains two emitters 360, SAR program 316 can calculate theposition of probe tip 301 through standard geometric computations. AfterSAR program 316 determines the respective positions of ring 306 andprobe tip 301 relative to array 300, it next determines the position ofring 306 relative to tip 301 within the probe coordinate system of FIG.2D.

One consideration in using sound emitters to determine position is thatthe speed of the emitted sound Will vary with changes in the temperatureof the air in the operating room. In other words, since the system isvery accurate, the period of time that it takes from the instant aparticular emitter 360 or 370 is energized to emit sound until theinstant that each of microphones 350 of array 300 receives the soundwill vary with air temperature. In order to calibrate the system forthese changes, temperature compensation emitter 304 is located in afixed position relative to array 300. Temperature compensation emitter304 may be, for example, a sonic digitizer as is used in the ScientificAccessories Corporation Model GP-8-3D. SAR program 316 knows, throughcalibration, the distance between temperature compensation emitter 304and each of the microphones 350 of array 300. The speed of soundtransmitted from temperature compensation emitter 304 to microphones 350is measured by the SAR program and compared against the known distanceto determine the speed at which the sound is being transmitted throughthe air. Therefore, SAR program 316 can immediately calculate thereference standard, i.e., the velocity of the emitted sound through theair. This instantaneous reference is applied to the sound emitted fromthe other emitters 360 and 370 to determine accurately the position ofthe other emitters.

After SAR program 316 has accurately determined the position of probetip 301 in the probe coordinate system shown in FIG. 2D, it outputs thecoordinates to translational software 318 in computer 314. Translationalsoftware 318 then translates the coordinates from the surgical probecoordinate system of FIG. 2D into the scanned image coordinate systemshown in FIG. 1D, as more fully described below. A memory 320 accessedthrough a local area network (LAN) 321 stores each of the images of thepreoperative scan according to the respective positions of the scanswithin the scanned image coordinate system of FIG. 1D. The respectivepositions of the scans are known from the position of rods 100 and 109in the scans, which information is stored in memory 320. The translatedcoordinates generated by translational software 318 are provided tostereotactic image display software 322, also resident within computer314. Stereotactic image display software 322 actuates a stereotacticimaging system 324 to generate a scan image from the data stored inmemory 320 corresponding to the translated coordinates. Stereotacticimaging system 324 displays the generated image on a high resolutiondisplay 326. Display 326 preferably displays the axial, saginal andcoronal views corresponding to probe tip 301. Stereotactic image displaysoftware 322 and stereotactic image system 324 may be any off-the-shelfsystem such as manufactured by Stereotactic Image Systems, Inc. of SaltLake City, Utah. This cycle of calibrating the system throughtemperature compensation emitter 304, sequentially energizing emitters370 and 360 to determine the respective positions of ring 306 and probe302, and generating and displaying a scan image corresponding to theposition of probe tip 301 all occur each time the surgeon closes aswitch to activate the system. The switch (not shown) may be positionedon probe 302, in a floor pedal (not shown), or wherever else may beconvenient to the surgeon.

As seen above, ring 306 is one apparatus for determining and positioningthe reference points RP1, RP2 and RP3 with respect to microphone array300. An advantage of ring 306 is that, each time emitters 360 on probe302 are energized, emitters 370 on ring 306 are also energized toredefine the reference plane. This allows the surgeon to move shepatient's head during surgery.

Alternatively, as shown in FIG. 3D, the reference points RP1, RP2 andRP3 can be established with the 3D digitizer 312 and three referencepins 307. Reference pins 307 are radiolucent surgical screws withradiopaque tips. pins 307 are permanently affixed to the patient's skullbefore surgery and before the preoperative scanning. The radiopaque tipsthereby provide a constant reference during scanning and throughout thestereotactic surgical procedure. During surgery, probe tip 301 ispositioned on each of pins 307 and actuated to emit a signal which isdetected by microphone array 300 and output to 3D digitizer 312. Thisallows the position of tip 301 to be determined at each of these points.This is performed during a reference mode of operation of 3D digitizer312. At the end of the reference mode, SAR program 316 calculates theposition of the reference points RP1, RP2 and RP3. The use of pins 307requires that the reference points have to be reestablished before theposition of probe 302 is determined to avoid changes in the referenceplane due to movement of the head. A further variation contemplates thatemitters 370 may each be separately mounted to pins 307 or other fixedstructures positioned at each of the reference points.

In summary, this process according to the invention is illustrated inFIG. 3C and identifies the location of probe tip 301 for the surgeon.Initially, the reference plane is determined by energizing ring 306 orby positioning probe tip 301 at the reference points. Next, the emittersof probe 302 are energized so that the position of probe tip 301 in thehead is determined in the probe coordinate system (X₂, Y₂, Z₂).Translational software 318 then converts the probe coordinate systeminto the scanned image coordinate system (X₀, Y₀, Z₀) so that the imagecorresponding to the position of probe tip 301 can be generated anddisplayed.

In another system of the invention as shown in FIG. 4A, infraredemitters 540 and 545 and an array 552 of detectors 550 are usedrespectively in place of sound emitters 360 and 370 and microphones 350of FIG. 3B. Fixed reference bar 548, a surgical probe 542, and relatedcomponents are used in place of ring 306, probe 302, and relatedcomponents of FIG. 3B. A Mayfield clamp 570 of known construction isused in place of ring 120 for rigid attachment to the patient's head394. Clamp 570 includes sharp pins 572 attached to adjustable jaws 574and 576. Clamp 570 is thereby adjusted for rigid attachment to head 394.Reference bar 548 is rigidly attached to clamp 570 so that there is norelative movement between bar 548 and head 394. No temperaturecompensating emitter such as emitter 304 in FIG. 3B is required in FIG.4A because the apparatus of FIG. 4A uses the position of emitters 540and 545 as viewed by detectors 550 (as more fully explained below) todetermine probe and ring positions instead of the time of transmissionof the emitted signal as with the embodiment of FIG. 3B.

In use, infrared detectors 550 are attached to a mounting bar 551 infixed relation to each other. Detectors 550 are generally positioned sothat their views converge on a phantom point. For example, the two outerdetectors 550L and 550R may view a field of two intersecting verticalplanes and the center detector 550C would view a horizontal plane. Thiscan be accomplished by employing vertical slits on the field of view ofthe outer detectors and a horizontal slit on the field of view of thecenter detector. The phantom point is set to be in the general vicinityof the patient's forehead 390. Mounting bar 551 is suspended from theoperating room light in direct line of sight of the patient's forehead390 and of emitters 540 and 545. Detectors 550 thereby detect theinfrared light emitted from emitters 540 and 545. Detectors 550 includea large number of linear chip cameras such as CCD (charge coupleddevice) cameras or pixels. A cylindrical lens (not shown) may also beused behind the slits in detectors 550 to collimate the infrared light.By knowing which particular pixel of the large number pixels found ineach of the three detectors 550 receives the infrared light fromemitters 540 and 545, the angle to a particular emitter from each ofdetectors 550 can be determined and, therefore, the positions of each ofemitters 540 and 545 can be determined using conventional mathematicalanalysis. Accordingly, the position of probe tip 541 within the scanimage coordinate system is known.

The apparatus of FIGS. 4A, 4B, 6A, 7 and 8 may be controlled with thecomputer and other hardware shown in FIG. 3A using the software shown inFIG. 5. Apart from the use of infrared light in place of sound and themeasurement of the position of the emitters through geometry instead ofthe timed delay of sound, the operation of this hardware and softwareparallels the operation disclosed above.

An advantage of using infrared light is that it allows for the use ofthe contour of a portion of the patient's head 394, preferably theforehead 390 above and around the patient's eyes, to relate the positionof the probe 542 to the scan images. This is accomplished with anoptical scanner 380 which generates an infrared laser beam which isreflected off of the patient's forehead 390 in timed sequence with thefiring of emitters 545 to determine the forehead contour relative toreference bar 548. Such optical scanning of the forehead allowspreoperative scanning to occur well in advance of anticipated surgeryand without intubation. Other benefits and features of the improvementare more fully explained below.

In particular, FIGS. 4A and 4B include infrared selector array 552,probe 542, reference bar 548 and optical scanner 380. Surgical probe 542preferably is a surgical coagulating forceps such as a bipolarcoagulating forceps. probe 542 could also be a drill, suction tube,bayonet cauterizing device, or any other surgical instrument modified tocarry at least two infrared emitters 540 thereon for determiningposition. Emitters 540 on probe 542 are essentially coaxial on an axis544 with tip 541. Emitters 540 are in line and immediately below thesurgeon's line of sight so that the line of sight is not blocked. Probe542 has a bundle of wire 364 attached thereto for connection to anelectrical power source. The wires required to energize emitters 540 arecombined with bundle 364. Bar 548 comprises a bar with a plurality of atleast three infrared emitters 545 positioned thereon. During surgery,the line of sight between some of the emitters 545 and the array 552 maybe blocked by a surgical hose or other object. This could temporarilyprevent array 552 from detecting the position of bar 548. Accordingly,it is preferable to place more than three emitters (e.g., seven or eightemitters) on bar 548 so that the line of sight for at least threeemitters is always maintained. Such additional emitters can also be usedto more precisely locate the position of bar 548. Bar 548 which holdsemitters 545 is also preferably positioned slightly away from head 394for increased clearance around head 394 and to reduce the number ofinstances where the line of sight between emitters 545 and array 552 isblocked. Optical scanner 380 is generally located in front of thepatient's forehead 390. Optical scanner 380 and its associated softwareto generate a forehead image are standard, off-the-shelf components suchas those used to scan an object to determine its three-dimensionalshape. For example, a limb scanner such as the PIXSYS Optical Scannerused to develop three-dimensional models for artificial limbs may beused.

During the preoperative scanning process, when the cross sectionalscanned images of the patient's head 394 are created, head 394 isfastened securely in a cushioned cradle 392 with surgical straps (notshown). If the contour of forehead 390 appears in the scan images, thencomputer 396 employs forehead fitting software 398 to derive theforehead contour from the scan images and to database the scan images asa function of the forehead contour in memory 320. If the scan images donot show the forehead 390, then (as shown in FIG. 7) head 394 is firmlyclamped in fixed relation with a reference source, such as a ring 590,having emitters 592 thereon. Optical scanner 380 is then used todetermine the position of the forehead contour relative to ring 590 (asmore fully described below). Because the position of the scan imagesrelative to ring 590 is known from the scanning procedure, the positionof the scan images relative to the forehead contour is known. Thisinformation is then databased in memory 320 and used during surgery torelate the position of probe 542 to the scan images.

Forehead scanning with optical scanner 380 is accomplished in thefollowing way. During preoperative scanning, head 394 is rigidlyattached to ring 590 in FIG. 7. This attachment may be accomplished witha base ring (not shown) such as ring 120 in FIG. 3B. Under the controlof 3D digitizer 312, scanner 380 emits an infrared laser beam whichbounces off a single point on forehead 390 and is detected by array 552.Computer 396 determines the position in space of this first point onforehead 390, such as by triangulation. Next, emitters 592 on ring 590are energized sequentially. Array 552 detects these emissions andcomputer 396 determines the relation between the first detected positionon forehead 390 and the position of ring 590. This process is repeatedmany times, with scanner 380 tracing a path across forehead 390. All ofthe data comprising the position of each point of reflection fromforehead 390 and the related position of ring 590 is input into foreheadfitting software 398 of computer 396. Computer 396 thereby determinesthe contour of forehead 390 and, thus, the position of the foreheadcontour relative to ring 590. Forehead fitting software 398 may be anyoff-the-shelf or custom software which graphs a set of points so that acurve defining the contour of the forehead can be calculated. Computer396 then outputs data relating the position of the forehead contour withthe position of ring 590 to translational software 318 of computer 314.During scanning, the position of the scan images relative to ring 590 isknown so that the position of the scan images relative to the foreheadcontour is also known. Accordingly, the scan images are stored in memory320 as a function of the forehead contour.

Prior to surgery, head 394 is clamped with a mechanism such as theMayfield clamp 570 shown in FIG. 4A for maintaining head 394 in rigidposition. Reference bar 548 is rigidly attached to clamp 570 withemitters 545 in line of sight with array 552. Optical scanner 380 nextscans the forehead to determine the position of the forehead contourrelative to bar 548. The forehead contour derived from this secondoptical scanning is matched to the forehead contour stored for thescanned images in memory 320 so that the current position of bar 548with respect to the scanned images is known. The forehead contourmatching between the stored forehead contour and the forehead contourderived from the second optical scanning is accomplished using the wellknown Pellazari Chen algorithm or any other suitable surface matchingalgorithm. Bar 548 used during surgery includes emitters 545 whichcommunicate with array 552 to establish the position of bar 548. Sincethe position of probe 542 relative to bar 548 is known (because ofcommunication via emitters 540 and 545 and array 552) and since theposition of bar 548 relative to the scanned images is known, theposition of probe 542 relative to the scanned images is known.Accordingly, a scanned image corresponding to the position of tip 541 ofprobe 542 is generated and displayed.

One advantage of using either optical scanner 380 or surgical pins 307in establishing a reference is that the reference ring, such as ring120, is removed after preoperative scanning and before surgery. This isadvantageous because the patient can not be intubated while ring 120 isattached to the skull. In the prior art, where ring 120 can not beremoved during the time between preoperative scanning and surgery, thepatient must be intubated (and therefore anesthetized) prior topreoperative scanning. Thus, by using the contour of forehead 390 todefine the reference point, the preoperative scanning is performedwithout the need for intubation and the anesthesia accompanying it. Thisis particularly advantageous during PET, MEG and any other type offunctional scanning where the patient must be conscious to elicitbehavior during scanning. It is also advantageous during any form ofscanning where the medical equipment for providing intubation andanesthetic would otherwise interfere with the scanning technology, suchas MRI scanning.

In summary, when CT scanning is used, the patient lies with the headheld in place on a CT table during the preoperative scanning process.The scans are organized in memory 320 according to the forehead contourappearing in the scans. Prior to surgery, the patient's head 394 isrigidly held in a Mayfield clamp or similar clamp on which reference bar548 is mounted. Optical scanner 380 is then used to determine thepatient's forehead contour relative to bar 548. Since the position ofthe scan images relative to the forehead contour is already known, theposition of bar 548 relative to the scan images is known. Duringsurgery, the surgeon positions probe 542 in the position desired withinhead 394. Emitters 540 of probe 542 and emitters 545 of bar 548 are thenenergized so that the position of probe tip 541 relative to bar 548 and,therefore, relative to the scan images is known. This is accomplishedthrough the translational software 318 which converts the probecoordinate system (X₂, Y₂, Z₂) into the scanned image coordinate system(X₀, Y₀, Z₀) so that the image corresponding to the position of probetip 541 can be generated and displayed.

Further summarizing, when MRI, PET or MEG scanning is used, the patientlies on an MRI, PET or MEG table with head 394 rigidly attached to ring590. Optical scanner 380 then scans forehead 390 to determine theposition of the forehead contour relative to ring 590. The MRI, PET orMEG scanning is then performed and the scan images are produced in knownrelation to the position of ring 590 and, therefore, in known relationto the forehead contour. The scans are organized in memory 320 accordingto the forehead contour. Prior to surgery, head 394 is rigidly held in aMayfield clamp or similar clamp on which reference bar 548 is mounted.Optical scanner 380 is then used to determine the patient's foreheadcontour relative to bar 548. Since the position of the scan imagesrelative to the forehead contour is already known, the position of bar548 relative to the scan images is known. During surgery, the surgeonpositions probe 542 in the position desired within head 394. Emitters540 of probe 542 and emitters 545 of bar 548 are then energized so thatthe position of probe tip 541 relative to bar 548 and, therefore,relative to the scan images is known. This is accomplished throughtranslational software 318 which converts the probe coordinate system(X₂, Y₂, Z₂) into the scanned image coordinate system (X₀, Y₀, Z₀) sothat the image corresponding to the position of probe tip 541 can begenerated and displayed.

Referring to FIG. 5, a flow chart of the operation of translationalsoftware 318 is shown as it is used with the apparatus of FIG. 3B.Initially, the surgeon locates probe 542 in the position which is to bedetermined. (If ring 306 is not being used to identify the location ofthe reference plane, the initial step is for the surgeon to use thereference mode of 3D digitizer 312 to identify the reference plane bylocating probe tip 541 at several points in the plane.) The system theninitializes at a step 400 so that translational software 318 opens awindow menu at a step 402 of a multitasking program such as DESQ VIEWdistributed by Quarterdeck Office Systems of Santa Monica, Calif. Suchsoftware permits simultaneous execution of multiple software programs.In general, once a program is selected for actuation, it continues torun either in the foreground or in the background until deactuated.

Translational software 318 continues initializing by selectingstereotactic imaging system 324 through stereotactic image displaysoftware 322 and actuating stereotactic imaging system 324 in theforeground by opening the stereotactic window at a step 404. Thereafter,translational software 318 returns to the window menu at a step 406moving stereotactic image display software 322 to the background andselects the digitizer window at a step 408 to actuate digitizer 312 inthe foreground. Computer 314 is then ready to be actuated by the footswitch.

The surgeon then actuates a foot pedal or other switch which indicatesthat the system should perform a computation. Actuation of the footswitch is essentially the beginning of a start step 410. Upon actuation,if sound transducers 360 and 370 and microphones 350 of FIG. 3B arebeing used, digitizer 312 initiates calibration through temperaturecompensation emitter 304 to determine the velocity of the sound waves inthe air, energizes emitters 370 of ring 306 to locate the referenceplane and energizes emitters 360 of probe 302 to locate the position ofprobe tip 301. The signals detected by microphone array 300 aredigitized so that SAR program 316 determines the coordinates of tip 301.At a step 412, translational software 318 selects the coordinates fromSAR program 316.

Next, the window menu is again accessed at a step 414 and the windowmenu switches stereotactic image system software 322 to the foregroundat a step 416 to specifically control the operation of stereotacticimaging system 324. At this point, translational software 318 issues anF1 command to stereotactic image display software 322 which in turnprepares stereotactic imaging system 324 to accept coordinates. At astep 420, the window menu is again selected so that at a step 422computer 314 switches the digitizer window into the foreground. At astep 424, the digitizer window menu is accessed and coordinatetranslation is selected. At a step 426, digitizer 312 begins calculatingthe coordinates and at a step 428 the coordinate calculation is ended.Translational software 318 then returns to the digitizer window menu ata step 430, switches windows to place stereotactic image system software322 in the foreground at a step 432 to prepare it for receiving thecoordinates and again returns to the main window menu at a step 434.Finally, the coordinate information is translated, including anynecessary manipulation, and transferred to stereotactic image displaysoftware 322 at a step 436 which actuates stereotactic imaging system324 to generate the particular image from memory 320 and display it onthe high resolution display 326. Stereotactic image display software 322instructs stereotactic imaging system 324 to display a cursor on display326 at the coordinates which corresponds to the position of probe tip301. Thereafter, computer 314 is in a standby mode until the foot switchof the surgeon is again actuated to execute translational software 318beginning with the start step 410.

The translation that occurs in step 436 depends on the position of theprobe coordinate system relative to the scanned image coordinate systemand the units of measure. The systems are preferably coaxial and theunits of measure the same so that algebraic adjustment is unnecessary.However, it is contemplated that the coordinates systems may not becoaxial, in which case translation would require arithmetic and/ortrigonometric calculations. Also, the sequence, e.g., (X₂, Y₂, Z₂), inwhich the coordinates are generated by the digitizer 312 may bedifferent than the sequence, e.g., (X₀, Y₀, Z₀), in which thestereotactic image system software 322 receives coordinates. Therefore,the sequence in which the coordinates are transferred may have to bereordered.

Those skilled in the art will recognize that the above computerprogramming could be accomplished in a number of other ways withoutdeparting from the scope of the invention. As one example, and apartfrom the use of multitasking programs and their associated windows andmenus, a personal computer could be directly programmed to calculate thecoordinates of the position of probe tip 301 for use in generating thescan image corresponding to the position of tip 301 from the data storedin memory 320.

The steps performed by translational software 318 for the system of FIG.4A are similar to those described above for the system of FIG. 3B withthe following exceptions. First, the system of FIG. 4A does not requirea calibration emitter such as emitter 304 in FIG. 3B so that thecorresponding step is skipped in the software for FIG. 4A. Further,infrared emitters 540 and 545 are used in place of sound emitters 360and 370 for determining the position of probe tip 541 and bar 548. Asabove, the various positions of the emitters are determined based on theangle of the view of detectors 550 to each of emitters 540 and 545. Theangle is known from knowing which pixel within each of detectors 550detects the infrared light. Still further, when the optical scanner 380is used, translational software 318 for the system of FIG. 4A includesadditional steps for operating optical scanner 380 through multiplexer310 to scan a series of infrared laser beams across forehead 390 fordetection by detectors 550. This data is received by digitizer 312 andpassed to computer 396 so that the forehead contour can be determinedthrough software 398. Data identifying the forehead contour is thenpassed back to translational software 318 for use as a reference.

Referring to FIG. 6A, a system of the present invention employing anultrasound localizer is illustrated. The ultrasound system includes amechanism such as a Mayfield head clamp 570 for maintaining head 394 inrigid position. Reference bar 548 is rigidly attached to clamp 570 asabove with emitters 540 in line of sight with array 552. The foreheadcontour is determined by optical scanning using optical scanner 380 andarray 552 of detectors 550 as shown in FIG. 4A and as more fullydescribed above. The ultrasound system also includes an ultrasound probe500 which may be used in the operating room to scan the brain.Ultrasound probe 500 includes a plurality of at least three noncolinearemitters 502 which are energized via a line 504 by multiplexer 310. Thesignal emitted by emitters 502 is received by array 552 to determine theposition of the body of ultrasound probe 500 relative to the position offorehead 390. This is accomplished through translational software 318which controls digitizer 312 and multiplexer 310 to energize emitters502 in a predetermined sequence to determine the position of the body ofprobe 500. This is the same technique used above in FIGS. 3B and 4A fordetermining the position of probes 302 and 542 and of rings 306 and 548.Ultrasound probe 500 is also connected via a line 506 to a system 508 ofknown construction which analyzes the ultrasound scanning and providesthe analyzed information to a monitor 510 which displays the ultrasoundimage. Since array 552 can determine the position of the body ofultrasound probe 500 at any point in time, via digitizer 312, theparticular plane of the image displayed on monitor 510 is known.

An ultrasound image is illustrated by way of example in FIG. 6B. Becausethe plane of the ultrasound scan image is known, the surgeon can signalstereotactic imaging system 324 to generate a scan image from adifferent scanning technology on display 326 which corresponds to theultrasound image. FIG. 6C illustrates such a corresponding image.Alternatively, system 508 may be linked to stereotactic imaging system324 directly via a data link 515 to communicate the position of the scanplane for the image shown on monitor 510 so that stereotactic imagingsystem 324 can automatically generate and display the correspondingscanned image for a different scanning technology on display 326. As aresult, the image from the ultrasound system, as illustrated on monitor510, is shown on one monitor and may be compared to a correspondingimage obtained from CT, MRI, PET, MEG or some other type of preoperativescanning. The cross section through the three dimensional data set asdeveloped by the ultrasound system is determined by a high speedgraphics system 508, such as manufactured by Silicon Graphics. Thisallows for better interpretation of the ultrasound scans as the anatomyfrom the MRI, CT, PET or MEG scans can be seen directly. Furthermore,the ultrasound system allows scanning in the operating room. Since thebrain tissue is elastic and the position of various tissue may changefrom time to time, use of an ultrasound scan in the operating roompermits a more definite localization of various brain tissues. Forclarity, ultrasound probe 500 is show in FIG. 6A as spaced away fromhead 394. Usually, ultrasound probe 500 is positioned in contact withthe skull during use. The probe may also be affixed to the skull duringsurgery for continual monitoring of the position of the brain.

FIG. 7 shows a system of the present invention for correlating the scanimages from different scanning technologies. A scanner 600 representsany of the several scanning technologies currently available (e.g. CT,MRI, PET, MEG) and is intended to include any other scanningtechnologies that may be developed. Scanner 600 scans head 394 in aplane 602. Plane 602 is usually defined visually by an array of lightbeams. If the pertinent scanning technology reveals the position of theforehead contour in the scan images, then computer 396 employs foreheadfitting software 398 to derive the forehead contour from the scanimages. Computer 396 organizes the scan images as a function of theforehead contour for storage in memory 320.

If the pertinent scanning technology does not reveal the position of theforehead contour in the scan images, then ring 590 is rigidly attachedto head 394. The optical scanner 380 is used prior to scanning to relatethe position of the forehead contour relative to ring 590 (as describedin the text accompanying FIG. 4A). Ring 590 lies in a plane 604. Duringscanning, planes 602 and 604 are preferably maintained in parallelrelation by initially aligning ring 590 coplanar with the visual arrayof light beams defining plane 602. However, it is not necessary toinitially align ring 590 coplanar with scan plane 602. As long as therelative relationship in space between ring 590 and plane 602 is knownand that relationship is maintained during tee scanning, the orientationof the forehead relative to the scan plane can be calculated. Since ring590 will appear in at least one scan and since the position of one scanwithin a group is known with respect to the other scans in the group,the respective positions of the scans relative to ring 590 is known.Since the position of the forehead contour relative to ring 590 wasdetermined by scanning the forehead with scanner 380, the position ofthe forehead contour relative to the scan images is known. Computer 396now employs forehead fitting software 398 to organize the scan images asa function of the forehead contour. This information is databased inmemory 320. The forehead contour is then used to relate the scan imagesof one technology such as PET to the scan images produced from any othertechnology such as CT, MRI, or MEG.

When the scan images from several technologies are available, it iscontemplated within the scope of the invention to use a like number ofdisplays to display each of the scan images corresponding to theposition of the probe 302 or 542, or to use a lesser number of displays,each showing multiple scan images. Likewise, it is contemplated that ascan image from one technology may be used as a reference in locatingcorresponding scan images from other technologies. Finally, while thisdisclosure broadly describes the use of the invention for scanning thepatient's head, it is contemplated within the scope of the invention touse the invention for scanning and analyzing other portions or the bodyof the patient.

FIG. B shows a laser depth finder 620 for use in scanning the foreheadcontour when the line of sight between optical scanner 380 and array 552in FIG. 4A is blocked. FIG. 8 includes a Mayfield clamp 570 for holdinghead 394 in fixed relation to a reference bar 548 having emitters 545thereon. Depth finder 620 may be any of the laser based depth finderscommonly available which are accurate to within the required tolerances.At least three emitters 622 are affixed to depth finder 620. Emitters622 are controlled via multiplexer 310 so that computer 314 candetermine the position of depth finder 620 in addition to the positionof bar 548. In operation, depth finder 620 emits an infrared laser beamwhich is reflected off of forehead 390 and detected by a detector withindepth finder 620. The circuitry inside depth finder 620 calculates thedistance between the illuminated point on forehead 390 and a referencepoint on depth finder 620 and outputs a signal corresponding to thecalculated distance via a line 624 to computer 314. Computer 314 thensequentially fires emitters 545 and 622 via multiplexer 310 to determinethe positions of bar 548 and depth finder 620. Accordingly, at the endof this first cycle, one point of the forehead contour can becalculated. This cycle is repeated a number of times until computer 314has obtained sufficient points to map the forehead contour.

FIGS. 9-11 show an alternative system for registering scan images withthe surgical space. FIG. 9 includes a cap 700 which fits snugly overhead 394. Cap 700 is secured by an adjustable strap 702. In use, thereshould be no relative movement between cap 700 and head 394. A pluralityof grommets 704 are sewn into cap 700 at regular intervals. FIG. 10shows one such grommet in greater detail and FIG. 11 shows thecross-section through FIG. 10 at the indicated line. As can be seen inthese figures, grommets 704 encircle and thereby reinforce fabric 706 ofcap 700. A hole 707 centrally positioned within each grommet 704 is cutinto fabric 706 and provides space for supporting a marker 708 and alsoprovides access to underlying skin 710 on head 394. Fabric 706 ispreferably elastic in nature. The hole 707 in fabric 706 is smaller thanthe external dimensions of marker 708 so that fabric 706 is stretchedslightly to hold marker 708. For example, hole 707 may be a slit withinfabric 706.

Markers 708 include an internal reservoir filled with a radiopaquesubstance which is detected by the scanner during scanning and whichappears on the scan images. For example, the markers for CT scanning arefilled with omnipaque, the markers for MRI scanning are filled withgadolinium, and the markers for PET scanning are filled with aradioactive tracer. The capacity of the reservoirs in markers 708 isdifferent for the different scanning technologies because each scanningtechnology has a different resolution. However, markers 708 preferablyhave a uniform external dimension so that the same cap 700 can be usedwith any of the different types of scanners and related markers. Markers708 are easily attached within and removed from fabric 706 to allowquick access for marking skin 710 underneath. This is also helpful forpatients who are undergoing more than one scanning procedure usingdifferent scanning technologies. When multiple scanning technologies areused, the markers for the different technologies may be attached tofabric 706 within the same grommets 704 so that the images produced bythe different scanners all show markers 708 in the same places. Markers708 preferably consist of clear plastic material such as polyethylenetubing filled with a contrast medium 710 in the center and sealed atboth ends with epoxy 712. Markers 708 can be either prefilled and sealedwith suitable contrast medium or fillable by needle puncture with thecontrast medium.

For cranial surgery, cap 700 is preferably made of fabric consisting of85% Dupont Antron Nylon and 15% Lycra Spandex. Although one size may fitmost patients, the cap 700 can be sized or shaped to specific patients.Three-quarter inch grommets 704 are sewn at routine intervals over theentirety of the cap. For surgery on other parts of the body, a flexiblematerial is used which fits snugly like an ace wrap bandage. Again,grommets 704 are sewn every one or two inches. As with cap 700, there isa hole in the fabric 706 in the center of each grommet for holdingmarkers 708.

In use, the patient is instructed to wash his/her hair and to not applyany hair spray, lotion, or other materials prior to scanning in order toprovide as oil-free of a surface as is possible. After cap 700 is snuglyfit over head 394 and secured with chin strap 702, the surgeon selectsat least three (preferably more) grommets 704 which will be used to holdmarkers 708. As accuracy of three point registration increases withgreater separation of markers, markers 708 are preferably placed overthe largest area available to insure a low margin of error. If surgeryis planned, hair surrounding the operative area can be clipped or leftin place as desired by the surgeon. A small amount of hair is clipped ordisplaced around the area where markers 708 will be used to allow thepositioning of markers 708 close to skin 710. Skin 710 is marked withindelible ink 716 through the holes in fabric 706 of the grommets 704 inwhich a marker 708 is to be attached. Markers 708 are then attached tosaid fabric. During this time, the surgeon carefully checks to insurethat each marker 708 is positioned adjacent to and directly over the inkmark 716 on skin 710. Ink mark 716 is preferably positioned in thecenter of the hole in fabric 706. The patient is then positioned on thescanning table and head 394 is scanned. After scanning, markers 708 areremoved. During removal of the markers, the surgeon carefully checks tosee that each marker did not move during scanning by checking to seethat each is still positioned adjacent to and directly over thecorresponding ink mark 716. Further, the ink marks should appear in thecenter of the holes in fabric 706. If a marker is no longer in positionadjacent the related ink mark and/or if the ink mark is not in thecenter of the hole, it indicates that movement of the marker hasoccurred some time during scanning. Accordingly, the particular ink mark716 and its corresponding marker 708 are not used during the subsequentregistration process where the scan images are registered with thesurgical space. If enough of the markers have moved from their positionsso that the position of three of the markers can not be confirmed, thenthe scan is repeated.

If scanning occurs immediately prior to surgery, the indelible ink marks716 may need no protection from the possibility of smudging oraccidental removal. The patient is issued a paper cap to wear until thetime of surgery and is instructed not to remove or interfere with theink marks. If there will be a delay between scanning and surgery, thereare several ways to assure the integrity of the indelible marks. Forexample, benzoin can be applied to the area surrounding the indeliblemark and allowed to dry. A strip of three-quarter inch transparent tapeis then applied to the area. Collodium may also be used in a similar wayto protect the marks.

After the integrity of at least three ink marks 716 has been confirmed,a three point solution utilizing directional cosines from two frames ofreference enables the surgeon to register the surgical space with thescan images. If the integrity of more than three marks 716 is confirmed,the additional marks can be used for redundancy to insure that theregistration was properly performed. The registration process can beaccomplished using the apparatus shown in FIGS. 4A and 3A. Inparticular, following scanning with cap 700 and markers 708, computer314 processes and stores the scan images in memory 320 as a function ofthe markers 708 which appear in the scan images using similar techniquesas those described above. Prior to surgery, head 394 is clamped in clamp394. The tip 541 of probe 542 is then touched on each of the ink marks716 on skin 710 of head 394 while the emitters 540 and 545 areenergized. Because computer 314 now knows the position of each of inkmarks 716 relative to reference bar 548, it can determine the positionof the scan images relative to reference bar 548. During surgery, asdescribed above, emitters 540 and 545 enable computer 314 to also knowthe position of probe tip 541 relative to reference bar 548.Accordingly, computer 314 knows the position of probe tip 541 relativeto the scan images. Computer 314 then generates a scan imagecorresponding to the position of tip 541. The generated image isdisplayed on display 326.

As can be seen, there are many advantages of using cap 700 and markers708 to register the scan images to the surgical space. For example, andunlike the placement of reference pins 307 in FIG. 3D, the placement ofmarkers 708 des not cause any pain to the patient. This is becausemarkers 708 are noninvasive and do not require the skin to be brokenwhen they are used. Accordingly, redundant markers are used whichprovide greater accuracy and which insure in most cases that at leastthree of the markers will be useable for registering the scan images.Another advantage is that routine scans can be taken with markers 708 inplace. If the initial scan locates a lesion that requires surgery, theposition of the scan images relative to markers 708 is known and thesame scan images can be used during surgery. Because of the paininvolved in implanting reference pins 307, however, they would rarely beused during routine scanning. If a lesion is found during such routinescanning, the entire scan has to be retaken again after pins 307 areimplanted. Yet another advantage of using markers 708 during scanning isthat they are removed prior to surgery and so they do not need to besterilized. Thus, the difficulty otherwise encountered in trying tosterilize such markers is avoided.

For surgery on parts of the body other than the head, a material withgrommets 704 sewn at regular intervals is wrapped once around the partbeing examined and attached with fasteners that do not distort the imageproduced. The material is applied snugly, like an ace wrap, withgrommets every one to two inches. Alternatively, the fabric can be madeinto a corset like structure, with the salient feature beingreinforcement with grommets that allow holes to be made in the fabricwithout weakening it, and that also allow placement of markers 708. Aswith cap 700, the skin is marked with indelible ink 716 under eachmarker. After scanning, marker 708 is removed and the skin mark 716 ischecked to insure that the marker has not moved.

Those skilled in the art will recognize that apparatus other than cap700 could be used for positioning markers 708 within the scope of theinvention. For example, markers 708 can be held in place adjacent an inkmark 716 using tape. Such transparent tape has been found to beparticularly effective in positioning markers on the forehead and otherhairless areas. Further, apparatus other than grommets 704 and fabric706 can be used to hold markers 708 within cap 700. Such other apparatusincludes any of the commonly found fasteners and mechanical fixturescapable of holding relatively small objects.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. A system for determining the position of a proberelative to a body of a patient, said system comprising:a receiverconfigured to receive signals; a reference fixed in relation to thebody, the reference in a line of sight with the receiver and thereference radiating and passing a signal representing the position ofthe reference to the receiver; a memory having stored images of thebody, the images including reference images correlatable to thereference; a probe in a line of sight with the receiver and the proberadiating and passing a signal representing the position of the probe tothe receiver; a processor in communication with the receiver and thememory, wherein the processor is configured to determine the position ofthe body in the images of the body, to determine the position of thereference relative to the receiver, to determine the position of theprobe relative to the receiver, to determine the position of the proberelative to the reference; to determine the position of the proberelative to the body, and to translate the position of probe relative tothe body to the position of the probe relative to the body in the imagesof the body; and a display of the images of the translated position ofthe probe relative to the body.
 2. A system for determining the positionof an instrument relative to a body of a patient, said systemcomprising:a base fixed in relation to the patient, the base radiating abase signal associated therewith; a memory having stored images of thebody, the images including reference images correlatable to the base; aninstrument radiating an instrument signal associated therewith; adigitizer in communication with the base and the instrument, thedigitizer configured to determine the position of the base and theinstrument based on the signals received from the base and theinstrument; a computer in communication with the digitizer and thememory, wherein the computer is configured to determine the position ofthe body in the images of the body, to determine the position of theinstrument relative to the base, to determine the position of theinstrument relative to the body, and to translate the position of theinstrument relative to the body to the position of the instrumentrelative to the body in the images of the body; and a display of theimages of the translated position of the instrument relative to thebody.